A variety of lasers have been used in modern dermatology for correction of inborn and acquired skin defects and diseases. One of the reasons for wide proliferation of the lasers in this field is that their properties are well support the principle postulate of medicine--"do not harm" a patient.
Drug therapy has been the most commonly used method of treatment in dermatology mainly because it is readily available, simple and less painful. However, drug intolerance, side effects, common allergic reactions as well as low efficiency in treatment of a substantial number of disorders often make this treatment less desirable.
A need for more efficient cure of dermatological defects and diseases made surgical involvement quite popular in this area of medicine. As to the surgical methods of treatment of skin disorders, doctors are often compelled to resort to such procedures as: dissection followed by transplantation, use of ultrasound and cryotherapy, application of magnetic fields of ionizing radiation, electrocoagulation, utilizing of plasma currents, etc. These surgical methods are used in spite of a great number of drawbacks and harmful side effects which include: destructive nature of the treatment, protractive healing process, high risk of hypopigmentation, possibility of atrophy, destruction of a skin texture, formation of scars, damage to an adjacent skin area including healthy regions. These problems are often alleviated when a surgeon uses local methods of treatment having short and fixed duration of action at a specified depth of a skin integument. This is one of the reasons why lasers have become recently the instrument of choice of many dermatologists.
Currently, lasers having different wavelength of laser irradiation are used in dermatology. Examples of such lasers are: excimer, ruby, argon laser; alexandrite and garnet laser; tunable semiconductor laser; etc. These devices generate laser beams having the wavelength in the visible range of the spectrum (0.4-0.7 m) as well as in the invisible, the UV range (0.18-0.40 m). For instance, infrared lasers include a set of CO.sub.2 lasers (with the wavelength of 10.6 m), variations of neodymium lasers (with the wavelength of 1.06 m), etc. These lasers are produced by Candela Laser Corporation and are described by "Lasers in Medicine" Tashkent, 1989.
In spite of the fact that these lasers maintain a short duration of action and provide certain localization in the plane of the action, they do not guarantee control of the treatment, especially as to the depth of penetration in the skin integument. Thus, use of these lasers does not eliminate such negative consequences as formation of hypotrophical scars and penetration of a laser beam into the area of healthy skin.
It is a matter of general knowledge that a layer of water practically does not allow optical irradiation at certain wavelength to pass therethrough. This region of the spectrum is typically known as the window of non-transparency and includes the following wavelength ranges: 1.25-1.40; 1.7-2.1; 2.5-3.1 and 5.5-7.5 microns. At these ranges optical irradiation is strongly absorbed by water and by living tissue which consists up to 90 percent water. Such absorption leads to a rapid heating of water and vaporization of the treated living tissue. At these wavelengths a laser beam acquires an important quality, that is that laser irradiation cannot penetrate deeply into living tissue substantially consisting of water. As a result, a scattered laser beam propagates in living tissue only within the range which does not exceed the depth of 15-20 microns and does not destroy adjacent tissue. Such a mode of operation of a laser can be implemented only at specific levels of power density and energy, predetermined rate and duration of the pulse and only when a temporary stability of all these characteristics is achieved during a surgical procedure.
One of such known devices is the aluminum-yttrium-erbium garnet laser having the wavelength of 2.94 m of laser irradiation. Initial reports about stomatological application of this laser appeared in 1989. However, its properties such as energy pulse of 1-2 J; the wavelength of 2.94 m and the pulse rate of 1 Hz enabled doctors to use this laser as surgical device in the field of dermatology. The first reports of such use became known in Germany and Slovenia in 1991.
A schematic diagram of FIG. 1 illustrates that such device consists of a power unit, a cooling unit, a laser cavity and an articulated mirror guide light unit. In view of the multiple reflection of the laser beam in the articulated mirror guide light unit the efficiency of the device is quite low and does not exceed 60 percents at the wavelength of 2.94 m. This makes it necessary to sustain energy input of the laser irradiation at the level 2.5-3.0 J and the operating power of the power unit at 300 W. Naturally, a laser of such high power has to have a very efficient cooling system. Therefore, a special water cooling system was provided in this prior art device. In view of that, the weight of the device was 70 kgs with overall dimensions of 0.5 m.sup.3. Thus, large weight and dimensions as well as instability of the laser beam characteristics greatly limited employment of this prior art laser in dermatology.
The water cooling system was necessary in the high powered prior art device to keep the temperature of the active element within 20.+-.10.degree. C. range. When this temperature range was exceeded the thermolens effect developed in the active element which resulted in considerable laser beam scattering and in the loss of energy in the focal plane of a treated tissue.
One way of resolving these problems is through the formation of more efficient laser system which lacks of the articulated mirror guide light and requires substantially less power. This makes possible the replacement of the water cooling system by its air cooling counterpart. Such changes ultimately lead to a substantial reduction of the weight and overall dimensions of the laser assembly.
Thus, there has been a considerable need for an efficient hand held laser surgical device usable in the field of dermatology which is capable of providing and controlling a predetermined depth of skin penetration and does not damage healthy regions of tissue adjacent the operation site.